Signaling system



Filed NOV 3, 1927 INVENTOR. .fatter A TTORNEY Patented Dec. l5, 1931 narran Astares' [raient arrives.

RALPH K. FOTTER, OF'JITEVI YORK, N. Y'., ASSIGNOR TO AIVERICAN TELEPHONE AND TELEGRAPI-I COMPANY, A CORPORATION F NIE-IV YORK sIGNALiNG Ysirs'iuiia Application filed November 3, i927. Serial No. 230,907.

rhis invention relates to signaling systems, and particularly to arrangements for signaling at high energy levels.

It has been determined by experiment 'that it is much more diiiicult toincrease the power output of a radio transmitter from, forexample, 100 kilowatts to, for example, 200 kilowatts, than it is to increase the power output from, for example, 5 kiloufatts'to 10 kilowatts. A point is finally reached at which it becomes practically impossible to 'increase the power output sufficiently and still provide suitable insulation. This is 'especially so-in signaling systems of the short wave type, since in this type of signaling system, circuit dimensions must necessarily be limited.

ri`here are other complications which limit the power to'be derived from a signaling system. In a system in which a battery of vacuum tubes are connected in parallel, the difficulty of operating at high power is familiar to those skilled in the art. In signaling systems of the long wave type, the expense of linge antenna structures is Very great. In

signaling systems of the short wave type, the

well-known troublesome inductive effects of powerful magnetic fields become apparent. In general, also, wherever the power output is increased, the breakdown hazard becomes greater and the margin of safety on insulation strength becomes reduced. Y

Itis the primary object of the present invention to provide a system, such as afra'dio telephone system, for the transmission of signals at high power, which system may be designed to greatly. overcome the difficulties mentioned hereinabove. f f Y Briefly, the system described herein, for illustrative purposes, consists in generating signals and subdividing these signals into sub-bands which may be components Vof the same side band of a high frequencyfcarrier wave, these sub-band components being transmitted through separate transmission channels. So far as the frequency spectrum is concerned, the same transmission channel is utilized as if a whole side band were radiated from a single source In other words', the sub-bands compose a. side band which occupies-no more space in the spectrum than would be occupied by that side band if it-were produced by modulating ordinaryspeech signals upon a carrier wave of a definite frequency. `At a distantvpoint such aside band may be received and combined with a single homodyiiing carrier wave, in amanner` well known in the art, since, ashas been stated hereinabove, the-separately radiated bands or sub-bands composing the side band are.r` all productsof modulation of the same carrier wave. 1 Interference, such as might be caused'- bythe transmission of signals from a pluralityiof separate sources, is reduced to a' minimum in this invention, as will be apparent from the description hereinafter following.

Assume, for illustration, that it is desirable' totransmit a. telephone conversation through space'over a single channel of, for example,

3000 cyclesin width and at a very high power level. Two transmitters, operating upon the same carrier wave, might be used in combination, the energy of the voice band representing the telephone conversation being suitably divided between these transmitters. Anapproximate division into v equal frequency ranges may, if desired, be obtained by the use of the well-known electrical wave iilters. Iflit becomes essential to divide the band representing the speech into sub-bands of substantially equalenergy levels, each transmitter may then also be provided with, for eX- ample, a level Aregulator which may, if desired, be' automatic in its operation, all of the regulators of the various transmitters then co-operating to equalize the power transmitted by the associated transmitters.

I The' various features and objects of'this invention will be better understood from the detailed description `hereinafter follow-V plified energy is then applied to another vacuum tube V2 through another transformer T2. After being further amplified, the speech signals are then applied through a transformer T3 to four sub-dividing electrical wave filters, F1, F2, F3 and F1. These electrical wave filters are preferably so designed as to pass adjacent portions of the speech frequency range. For example, filter F1 may selectively transmit frequencies from 200 to 800 cycles; filter F2 may transmit frequencies from 800 to 1400 cycles; filter F3 may transmit frequencies from 11100 to 2000 cycles; and filter F1 may transmit frequencies from 2000 to 2600 cycles, it being assumed that the essential speech frequencies are to be found within the range extending 'from 200 to 2600 cycles. This result vmay be accomplished by constructing each of these filters in the form of the well-known band filter, composed of a plurality of sections, as disclosed in a patent to Gr. A. Campbell, 1,227,113, dated lMay 22, 19,17. It will be obvious that a different number of filters than thev four illustrated may be used if desired, in which case the band widths of the respective filters will be suitably chosen to correspond with the number of filters used. It will be further understood that the filters already described herein are employed for the purpose of sub-dividing the speech frequency band into a plurality of sub-bands each of a relatively narrowr frequency range. Each of these subbands, if received, may, of itself, normally be incapable of providing intelligible signals.

With the arrangement of the four filters shown in the drawing, it will be seen thatthe lowermost sub-band is'transmitted by the filter F1. The next higher sub-band, beginning substantially at the upper limit of the first sub-band, is transmitted by the filter F2. Also, the next higher sub-band, beginning substantially at the upper limit lof the Vfrequency range of the filter F2, is transmitted by the filter F3, and the highest of the four sub-bands is transmitted by the filter F1.

These filters, therefore, transmit sub-bands which are adj acent in the frequency spectrum and, if combined, represent a band of signals corresponding to the speech signals originating in the microphone S.

The sub-bands transmitted bythe filters F1, F2, F3 and F1 are then applied to corresponding duplex modulators M1, M2, M3 and M1, respectively. For illustrative purposes the normal path of transmission of one of the sub-bands, namely, the sub-band transmitted by the filter F1, will be described herein in somewhat greater detail. The output of the filter F1 is applied through a transformer T.1 to the input circuits of a pair of vacuum tubes V3 and V1, which are in push-pull relation- Vthe vacuum tubes V3 and V1.

' ship. An oscillator O transmits current of a carrier wave through a transformer T3 to the branch common to the input circuits of The output circuits of these vacuum tubes are in parallel relationship with respect to a common plate battery, these output circuits being connected through the primary of a transformer TG. In-

asmuch as modulator M1 is supplied by a Wave of a carrier frequency by means o-f the oscillator O, and is also supplied with a subband, such as is transmitted by the filter F1, there will therefore be produced two side bands, each resembling the sub-band, though raised in the frequency spectrum, as is well known in the art. The modulator M1 may be of the general type disclosed in a patent to J. R. Carson, 1,343,306, dated June 15, 1920. The oscillator O may, of course, be of any Well-knowntype, preferably of the vacuum tube type, such as is shown and described in the patent to R. V. L. Hartley, 1,356,763, dated October 26, 1920 and vit may produce current of any frequency as, for example, 50,000-cycle current.

It will be apparent that the sub-bands transmitted by the filters F2, F3 and F1, are similarly applied to modulators M2, M3 and lifMrespectively, and that these modulators are also supplied by current of a carrier Wave from the same source, i. e., oscillator O, so that there may be similarly produced for transmission two side bands corresponding to each sub-band. Accordingly, two side bands are transmitted by each of the modulators M2, M3 and M1.

The modulators M1, M2, M3 and M,1 are connected to filters F11, F12, F13 and F11, respectively, each of these filters preferably having a band width substantially the same as the band width of the filter in the same transmission path. In other words, the band of frequencies transmitted by each of the iiltersv F11, F12, F13 or F11, is substantially equal in Width to the band of frequencies freely transmitted by the correspondingfilter F1, F2, F3, or F1. .Filters F11 to F11, inclusive, may, if desired, be ofthe' type described in the aforementioned Campbell patent, each freely transmitting one of the side bands corresponding to one of the sub-bands resulting from modulation, While substantially suppressing the other side band corresponding to the same sub-band as well as all other intermodulation components. Each of these filters may, if desired, be designed so as to suppress the lower side band and freely transmit the upper side b and, the upper side band being obviously `of a width substantially equal to the width of the sub-band freely transmitted by the filter in the same transmission path, though raised in the frequency spectrum as a result of modulation.

Thus, Vfilter 1l may selectively transmit frequencies from, for example, 50,200 to 50,800 cycles; filter 12 may transmit frequencies from 50,800 to 51,400 cycles; filter 13 may transmit frequencies from 51,400 to 52,000 cycles; and filter 141 may transmit frequencies from 52,000 to 52,600 cycles.v

Filters F11, F12, F11 and F11 are connected to amplifiers A1, A2, A, and A1, respectively. Each of these amplifiers may be of any wellknown type, preferably of the vacuum tube typeV shown in some detail in the transmission path transmitting the side band correspending to the lowest sub-band. The output of lter F 11 is applied through a transformer TT to a vacuum tube V5. After amplification by the vacuum tube V5, the band of signals is transmitted to another vacuum tube V6 through a transformer TS. After being again amplified, the band of signals is impressed through a transformer T1, upon the primary winding of a transformer T11. lt will be obvious that the amplifiers 1151111 and A1 may be of the same general type as the amplifier A1, and that each of theseV amplifiers employed to amplify the band of signals freely7 transmitted by the lilter in the same transmission path. Moreover, the band of signals am- Y plified by ampliiiers A2, A3 and A1 are also similarly impressed upon the primary wind-V ings of transformers T12, T13 and T11, respectively. The secondary windings of `transformers T11, T12, T13 and T11, are inseries with transmitting antennas TA1, TAZ, TA1, and TA1, respectively, so that the bands of signals impressed upon the primary windings of transformers T11, T12, T13 and T11 may be radiated through space by the transmitting antennas TA1, TAZ, TAS and TA1, respectively.

It will be apparent that by dividing the total power output of a signaling system into a plurality of elemental portions for their separate transmission to a distant station, which power output may also result froml the modulation of voice frequency signals upon a carrier wave, the insulation difficulties above mentioned are greatly reduced, especially as the power output becomes considerably increased. The inductive eects, due particularly to excessive magnetic fields, are minimized, and this is so especially in the case employing carrier waves of short length for modulation. Moreover. the difficulties apparent in the use of a large number of vacuum tubes in parallel forthe production of high power transmission systems are similarly minimized Furthermore, a failure in the transmission through one of the transmission paths will not completely paralyze the trans- Y mission of signals as a whole. And furthermore, the electrical amplifiers and antenna structures can be more sharply tuned, so that there will be less energy absorption than if they were broadly tuned.

It will be obvious that the system described herein may be applied to a transmission system for secret signaling in whicha normal speech band may be divided Vinto a plurality of subebands, which may be inverted and rearranged- .as desired and then modulated upon the same carrier wave in accordance with the principles outlined this invention. Clearly, one orv more of saidl sub-bands may be radiated from separate sources or interchanged .as desired, and then vradiated through space, within the scope of this invention. Y .Y f

It will be apparent that while this invention has been .described with particular reference to the sub-division of speech frequencies into a` plurality ofsub-bands of subtantially equalwidths, the 'sub-bands may, if desired,bey of unequal. widths and these widths maybe chosenso that the energies contained in the various sub-bands are approximately the same. Automatic level regulators may be .inserted beyond the filters F1, F2, F3 and F1 in order to suitably dividethe voice bandinto sub-bands of width depending upon energy levels.

While this invention hasbeen shown and described in one particulary embodiment, merely for the purpose vof illustration, it is to be distinctly understood that the general principles of this invention may be applied to other and widely varied organizations without departing from the spirit of the in- 1 vention and the scope of the appended claims.

`What is claimed is: i 1. The method of transmitting a band of waves at a high energy level, which comprises dividing said band into a plurality of separate sub-bands, modulating the same carrier wave individually by said sub-bands so as to produce a plurality of vside bands two of which correspond to each sub-band, and separately transmitting only the lower side bands of the various products of modulation as individual bands to a distant station.

2. In a high power short wave signaling system, the method of transmitting a band of waves corresponding to speech signals, which comprises dividing said band into a plurality of sub-bands, modulating each of said subbands upon the same carrier wave to produce corresponding, separate side-bands raised 1n the frequency spectrum, said side bands being adjacent to each other and together occupying the same width inthe frequency spectrum as the speech band before division, and separately transmitting the latter side bands to a distant point each at a lower power level.

3. In a high power short wave signaling system, the method of transmitting speech signals through space, which comprises di-` viding said speech signals into sub-bands of substantially equal energy levels, separately modulating each of said sub-bands simultaneously upon a particular carrier wave, suppressing the products of each modulation eX- cept one side band corresponding to each subband, and separately transmittingv the unsuppressedV side bands through space.

4. 'The method off transmitting speech signals at high energy levels, comprising subdivicling the speech signals into sub-bands of frequency components, the componentsv of each sub-band occupying a definite position in the frequency spectrum, simultaneously modulating a carrier Wave by said sub-bands in channels individual to each sub-band, suppressing tlie unmoclulated carrier component and one of the two side bands corresponding to each sub-bandi resulting from modulation, and separately transmitting the unsuppressed sifle bands corresponding to the subbancls to a distant point. i

In testimony whereof, I have signed my name to thisspecificationV this 18th day of October, 1927.

RALPH K.. POTTER.- 

